1. The oldest known ruler is over 4,000 years old. Discovered in the ancient city of Lothal (in modern-day India), the earliest ruler was made of ivory and had markings measured out with incredible scientific precision!

2. A foot ruler used to be based on a real king's foot. Before standard metric systems existed, people used body parts to measure things. Legend says King Henry I of England declared in the 1100s that a "foot" should be the exact length of his own right foot!

3. The word "ruler" has a double meaning for a reason. In ancient times, powerful kings and queens (rulers of a kingdom) set the official laws and standard measurements for their land. Over time, the straight sticks marked with those official measurements were named "rulers" too!

4. Flexible bendy rulers use special silicone. Modern plastic rulers that you can twist and fold into loops without breaking are made of flexible PVC or silicone rubber that "remembers" its flat shape when you let go.

5. A "standard" classroom ruler is 30 centimeters long. On the metric side of a standard 12-inch ruler, you'll find 30 centimeters (or 300 millimeter lines). Because 1 inch is equal to about 2.54 centimeters, a 12-inch ruler is almost perfectly equal to 30.5 centimeters!

6. Space scientists use lasers instead of wooden sticks. When NASA measures the exact distance from the Earth to the Moon, they can't use a giant measuring stick! Instead, they bounce laser beams off special mirror reflectors left on the Moon by Apollo astronauts to measure the distance down to the millimeter.

7. 12 inches equals 1 foot because of ancient counting. Ancient civilization mathematicians liked the number 12 because it could easily be divided into halves, thirds, and quarters (12÷2=6, 12÷3=4, 12÷4=3). This made splitting up land, wood, and cloth simple without using tricky fractions!